1. Field of the Invention
This invention relates to particulate material comprising a binder, and a method for making same. When the particulate material further contains abrasive grits, it can be used in bonded abrasives, coated abrasives, and nonwoven abrasives.
2. Discussion of the Art
Conventional coated abrasive articles typically consist of a layer of abrasive grits adhered to a backing. Generally only a small fraction of the abrasive grits in this layer are actually utilized during the useful life of the coated abrasive article. A large proportion of the abrasive grits in this layer are wasted. Furthermore, the backing, one of the more expensive components of the coated abrasive article, must also be disposed of before it has worn out.
Many attempts have been made to distribute the abrasive grits on the backing in such a manner so that a higher percentage of abrasive grits are actually utilized, thereby extending the useful life of the coated abrasive article. By extending the life of the coated abrasive article, fewer belt or disc changes are required, thereby saving time and reducing labor costs. Merely depositing a thick layer of abrasive grits on the backing will not solve the problem, because grits lying below the topmost grits are not likely to be used.
Several methods whereby abrasive grits can be distributed in a coated abrasive article in such a way as to prolong the life of the article are known. One such way involves incorporating abrasive agglomerates in the coated abrasive article. Abrasive agglomerates consist of abrasive grits bonded together by means of a binder to form a mass. The use of abrasive agglomerates having random shapes and sizes makes it difficult to predictably control the quantity of abrasive grits that come into contact with the surface of a workpiece. For this reason, it would be desirable to have an economical way to prepare precisely shaped abrasive agglomerates.
This invention provides precisely shaped particles and methods for making these particles. The particles comprise a binder. In one desirable embodiment, a plurality of abrasive grits is dispersed in the binder.
The method of this invention comprises the steps of:
(a) providing a production tool having a three-dimensional body which has at least one continuous surface, the surface containing at least one opening formed in the continuous surface, with at least one opening providing access to a cavity in the three-dimensional body;
(b) providing a dispensing means capable of introducing a binder precursor comprising a thermosetting resin into said at least one cavity through said at least one opening;
(c) providing a means, within a curing zone, for at least partially curing said binder precursor;
(d) introducing said binder precursor into at least a portion of said at least one cavity;
(e) continuously moving said at least one cavity through said curing zone to at least partially cure said binder precursor to provide a solidified, handleable binder having a shape corresponding to that portion of the cavity into which the binder precursor had been introduced;
(f) removing said binder from said at least one cavity; and
(g) converting said binder to form a precisely shaped particle.
Steps (f) and (g) can be conducted simultaneously.
In a preferred embodiment, a plurality of abrasive grits is included with the binder precursor in step (d), and a binder containing abrasive grits is formed in step (e). The binder that contains abrasive grits is removed from the at least one cavity of the production tool in step (f). Materials other than abrasive grits can be included with the binder precursor.
The curing zone can contain a source of thermal energy, a source of radiation energy, or both. Suitable sources of radiation energy include electron beam, visible light, and ultraviolet light. In a variation of the general method, curing can be effected by thermal energy or by a combination of radiation energy and thermal energy.
In both the general and preferred embodiments, it is preferred that steps (d), (e), and (f) be carried out on a continuous basis or be carried out in a continuous manner. For these embodiments, it is preferred that the production tool be an endless web (belt), or a drum, preferably a cylindrical drum, which will rotate about its axis. Alternatively, a web having two ends can be used. Such a two-ended web travels from an unwind station to a rewind station. It is preferred that the production tool have a plurality of cavities.
During step (e) of the method, the binder precursor is solidified so as to be converted into a handleable binder.
The binder can be converted into particles by several means. In one means, when the binder is removed from the cavities of the production tool, it is released in the form of individual particles. These particles can contain additional materials or be free of additional materials. A typical material that can be included in these particles is abrasive grits. The resulting particles preferably have shapes that are essentially the same as the shapes of the cavities of the production tool. Thus, the particles have shapes that are determined by the shapes of the cavities of the production tool. In this first means, steps (f) and (g) are accomplished simultaneously, because the shaped particles have their characteristic form when they are released from the cavities of the production tool.
In a second means, the binder is removed from the major surface of the production tool in the form of a sheet comprising shaped portions that are of essentially of the same size and shape of the cavities of the production tool, but joined together by a relatively thin connecting layer of the material of the binder. In this second means, the sheet is then broken or crushed along the thin connecting layer of binder material to form the particulate material of this invention. The particles can be screened or classified to remove any undesired particles. If the connecting layer of the binder material is carefully broken or crushed, the resulting particles can have shapes that are essentially the same as those of the cavities of the production tool.
It is also within the scope of this invention to use a carrier web to deliver binder precursor to the production tool. The binder precursor can be coated onto one major surface, e.g., the front surface, of a carrier web and then the resulting coated carrier web is brought into contact with the continuous surface of the production tool that contains the cavities. After at least partial curing, i.e., solidifying, of the binder precursor in the production tool, the binder, which preferentially adheres to the surface of the carrier web, is removed first from the production tool and then from the carrier web. Alternatively, the binder precursor is coated onto the continuous surface of the production tool having cavities, whereby such cavities are filled, and the carrier web is brought into contact with the continuous surface of the production tool containing the binder precursor in such a manner that the binder precursor contained in the cavities contacts the surface of the carrier web. After at least partial curing, i.e., solidifying, of the binder precursor, the binder adheres to the surface carrier web rather than to the production tool. The binder can then be removed from the carrier web. Subsequently, the precisely shaped particles are formed.
The precisely shaped particles can be modified by means of additives for use in abrading applications, either by themselves or as a component of an abrasive article. The particles of this invention can be used to prepare abrasive articles comprising a plurality of shaped particles, each of which comprises at least one abrasive grit and a binder, in which the binder is formed from a binder precursor comprising a thermosetting resin that can be cured by radiation energy or thermal energy or both. The particles can be bonded together to form a shaped mass, e.g., a wheel; alternatively, the particles can be bonded to a backing to form a coated abrasive article; or the particles can be bonded into a fibrous, nonwoven substrate to form a non-woven abrasive article.
This invention makes it possible to design particles suitable for specific applications by varying the shape and composition of the particles. The process of this invention provides a simple, fast, and economical method for manufacturing particles, especially abrasive particles having a precise shape. The process of this invention makes it possible to accurately make abrasive particles having the same dimensions from batch to batch, thereby leading to more consistent abrasive articles.
Another aspect of the invention pertains to a coated abrasive article, comprising:
(a) a backing having a front and back surface;
(b) a make coat present on the front surface of the backing;
(c) an abrasive layer bonded to the front surface of the backing by means of the make coat, wherein the abrasive layer comprises:
(1) a plurality of abrasive grits;
(2) a plurality of precisely shaped grinding aid particles, wherein the precisely shaped grinding aid particles comprise a binder and a plurality of grinding aid particulates; and
(d) a size coat present over the abrasive layer.
In general, it is preferred that the surface area of the abrasive layer comprises 5 to 90 percent, preferably 10 to 75 percent, most preferably 20 to 40 percent precisely shaped grinding aid particles.
Another aspect of the invention pertains to a bonded abrasive article, comprising:
(a) a bonding medium;
(b) a plurality of abrasive grits;
(c) a plurality of precisely shaped grinding aid particles, wherein the precisely shaped grinding aid particles comprise a binder and a plurality of grinding aid particulates; and wherein the bonding medium serves to bond the abrasive grits and precisely shaped grinding aid particles together to form a shaped mass.
It is preferred that the bonded abrasive is in the form of a wheel, including a cut off wheel. In general, the volume percent of the precisely shaped grinding aid particles in a bonded abrasive ranges from about 5 to 85 percent, preferably between 5 to 75 percent, more preferably between 5 to 60 percent and most preferably between 10 to 60 percent.
The precisely shaped grinding aid particles may further comprise abrasive grits. The abrasive grits will generally have a Moh hardness greater than about 8. However, it is generally preferred that the precisely shaped grinding aid particles consist essentially of the binder and grinding aid particulates.
Still another aspect of the invention pertains to a precisely shaped abrasive particle, comprising:
(a) a binder, wherein the binder is formed from a binder precursor comprising a resole phenolic resin and a free radically curable resin;
(b) a plurality of abrasive grits distributed in the binder to form the precisely shaped abrasive particle.
This type of precisely shaped abrasive particle can be incorporated into a coated abrasive article, a bonded abrasive article or a nonwoven abrasive article.
A further aspect of the invention pertains to an abrasive article comprising:
(a) a bonding medium, wherein the bonding medium having a plurality of precisely shaped filler particles distributed in a cured resinous adhesive, wherein the precisely shaped filler particles comprise a plurality of filler particles distributed in a binder;
(b) a plurality of abrasive grits,
wherein the bonding medium serves at least one of the following functions:
(1) to bond the abrasive grits to a backing;
(2) to bond the abrasive grits into and onto a nonwoven substrate; and
(3) to bond the abrasive grits together to form a shaped mass.
Another perspective of the invention pertains to a coated abrasive article, comprising:
(a) a backing having a front and back surface;
(b) a make coat present on the front surface of the backing;
(c) a plurality of abrasive grits bonded to the front surface of the backing by means of the make coat; and
(d) a size coat present over the abrasive grits, wherein at least one of the make or size coats comprises a plurality of precisely shaped filler particles distributed in a cured resinous adhesive, wherein the precisely shaped filler particles comprise a plurality of filler particles distributed in a binder.